1. Field of the Invention
The present invention relates to pipe couplings and more particularly concerns new and useful improvements in elastic gasket-type pipe couplings designed for use in connecting sections of pipe of the type typically employed in commercial and domestic sewage, sanitation, and similar plumbing systems operating with or without internal pressure.
2. Description of the Prior Art
Commercial and domestic plumbing systems, such as those used for sewage, sanitation, and the like, generally employ sections of pipe joined together in end-to-end relationship with some form of leak-proof coupling. Often these pipe sections are made from inexpensive cast iron with wide external pipe diameter tolerances and irregular surface features.
Several different pipe coupling assemblies have been proposed for joining pipe segments in end-to-end relationship. One convenient and successful coupling assembly is that described in U.S. Pat. No. 3,233,922 wherein a cylindrical elastic gasket is positioned around abutting pipe ends with a flexible corrugated metallic compression band wrapped around the elastic gasket and two or more hose clamps in turn positioned around the outside of the metallic compression band to secure the coupling assembly to the pipe ends. This elastic gasket-type pipe coupling, however, does not provide a leak-proof seal in many pressurized plumbing systems. Sewage lines within a high-rise commercial building, for example, will develop sufficient pressure over the space of a few stories to induce leakage of prior art elastic gasket-type couplings in vertically-oriented pipe structures.
In turn, none of the prior art devices employed in coupling pipe segments within a pressurized plumbing system enjoy the ease of installation and widespread utility of the elastic gasket-type pipe coupling. Threaded joints, the most common type of pressurized pipe coupling, require relatively thick pipe walls from which to form pipe threads, and further require special sealing compounds to provide a leak-proof seal. Thicker walled pipes, however, raise the cost of plumbing systems, and complicate the problem of securing the plumbing system within a building structure. Welded joints are also commonly employed as pressurized plumbing system pipe couplings. Welded joints, however, cannot be dismantled, require welding expertise on the part of the plumbing system installer, and create a fire hazard during installation and repair. This last consideration is a particular disadvantage in plumbing systems intended for use with flammable fluids or gases.
Previous attempts to modify elastic gasket-type pipe couplings for use in pressurized plumbing systems have met with limited sucess. One approach, illustrated in U.S. Pat. No. 3,359,017, focused on a means of applying greater compression forces to the corrugated metallic compression band and underlying gasket of an elastic gasket-type pipe coupling. Corrugations on a trailing edge of the metallic compression band were tapered off so as to terminate in a smooth planar surface. This structure avoided an interlocking of corrugations between overlapping portions of the metallic compression band which had previously hindered compression of the underlying elastic gasket. The greater compression forces more firmly sealed the elastic gasket to the outer surfaces of the abutting pipe ends. Due to surface irregularities common to the outer surfaces of castiron pipes, and the inexact placement of hose clamps compressing the coupling assembly, however, this approach provided a leak-proof coupling only in lightly pressurized plumbing systems.
Another approach, disclosed in U.S. Pat. No. 4,101,151, replaced the corrugated metallic compression band of the prior art with a slotted compression band having a raised central portion and flanged edges. This pipe coupling, however, could be used only in conjunction with pipe segments having an annular outwardly projecting hub on the outer suface of each pipe end, thus precluding the use of this pipe coupling with the more commonly available hubless cast iron pipe segments. This hub requirement further precluded use of the '151 pipe coupling in conjunction with "cut-to-fit" plumbing system assembly techniques.
Still another effort, disclosed in U.S. Pat. No. 3,581,901, required the use of pipe segments having an annular groove cut into the outer surface of each pipe end. This annular groove requirement, however, gives rise to the same limitations in application as encountered with the '151 pipe coupling.